The standard size for a twin mattress is 39 inches wide by 75 inches long. The extra-long twin mattress size, also know as a twin XL, is 39 inches wide by 80 inches long. When discussing mattress size, the term "single" is equivalent to "twin." Note that because of differences among manufacturers, the actual size of a specific twin mattress can vary by an inch in any dimension.
Twin mattresses are most commonly used in children's rooms. Twin XL mattresses are more comfortable for an adult sleeper, and are frequently used in college dormitory rooms.
Mattress depth is quite variable since extra-depth mattresses entered the market. Standard depth is 7 to 9 inches; a deep or pillow-top mattress is 10 to 15 inches high. Mattresses that are 15 to 22 inches deep are considered extra depth. This does not include the box springs, which are typically 8 inches high.
Mattress weight depends upon materials and depth. A standard-depth twin mattress with innerspring construction weighs about 50 pounds and increases to 75 pounds for deep twin mattresses. Twin mattresses constructed of latex and memory foam are heavier because the material is dense. A twin mattress made of latex foam can weigh between 60 pounds for standard depths and 100 pounds for a 12-inch depth. Twin XL mattresses made of latex foam weigh between 65 and 105 pounds for similar depths.
To allow the box spring to fit inside the bed frame, the outer dimensions of the bed frame are 1 to 4 inches greater in length and width than the mattress and springs. The height of the lower edge of the frame, where the box spring rests, is 10 to 11 inches above the ground. For a standard-depth mattress, the top of the headboard is typically 30 to 36 inches, and the top of the foot board is 24 inches above the ground.